The present invention relates to a novel rapeseed line designated 45A55 which is the result of years of careful breeding and selection. Since such line is of high quality and possesses a relatively low level of erucic acid in the vegetable oil component and a relatively low level of glucosinolate content in the meal component. It can be termed “canola” in accordance with the terminology commonly used by plant scientists.
The goal of plant breeding is to combine in a single variety or hybrid various desirable traits. For field crops, these traits may include resistance to diseases and insects, tolerance to heat and drought, reducing the time to crop maturity, greater yield, and better agronomic quality. With mechanical harvesting of many crops, uniformity of plant characteristics such as germination and stand establishment, growth rate, maturity, and plant and pod height, is important.
Field crops are bred through techniques that take advantage of the plant's method of pollination. A plant is self-pollinated if pollen from one flower is transferred to the same or another flower of the same plant. A plant is sib-pollinated when individuals within the same family or line are used for pollination. A plant is cross-pollinated if the pollen comes from a flower on a different plant from a different family or line. The term “cross-pollination” used herein does not include self-pollination or sib-pollination.
The creation of new superior, agronomically sound, and stable high yielding cultivars of many plant types including canola has posed an ongoing challenge to plant breeders. In the practical application of a chosen breeding program, the breeder often initially selects and crosses two or more parental lines, followed by repeated selfing and selection, thereby producing many unique genetic combinations. The breeder can theoretically generate billions of different genetic combinations via crossing, selfing and mutagenesis. However, the breeder commonly has no direct control at the cellular level of the plant. Therefore, two breeders will never independently develop the same line having the same canola traits.
Each year, the plant breeder selects the germplasm to advance to the next generation. This germplasm is grown under unique and different geographical, climatic and soil conditions, and further selections are then made during and at the end of the growing season. The characteristics of the lines developed are incapable of prediction in advance. This unpredictability is because the selection occurs in unique environments, with no control at the DNA level (using conventional breeding procedures), and with millions of different possible genetic combinations being generated. A breeder of ordinary skill cannot predict in advance the final resulting lines that are to be developed, except possibly in a very gross and general fashion. Even the same breeder is incapable of producing the same line twice by using the same original parents and the same selection techniques. This unpredictability commonly results in the expenditure of large research monies and effort to develop a new and superior canola line.
Canola breeding programs utilize techniques such as mass and recurrent selection, backcrossing, pedigree breeding and haploidy. For a general description of rapeseed and Canola breeding, see R. K. Downey and G. F. W. Rakow, 1987: Rapeseed and Mustard. In: Fehr, W. R. (ed.), Principles of Cultivar Development, 437-486. New York: Macmillan and Co.; Thompson, K. F., 1983: Breeding winter oilseed rape Brassica napus. Advances in Applied Biology 7: 1-104; and Oilseed Rape, Ward, et. al., Farming Press Ltd., Wharefedale Road, Ipswich, Suffolk (1985), each of which are hereby incorporated by reference.
Recurrent selection is used to improve populations of either self- or cross-pollinating Brassica. Through recurrent selection, a genetically variable population of heterozygous individuals is created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. Breeding programs use backcross breeding to transfer genes for a simply inherited, highly heritable trait into another line that serves as the recurrent parent. The source of the trait to be transferred is called the donor parent. After the initial cross, individual plants possessing the desired trait of the donor parent are selected and are crossed (backcrossed) to the recurrent parent for several generations. The resulting plant is expected to have the attributes of the recurrent parent and the desirable trait transferred from the donor parent. This approach has been used for breeding disease resistant phenotypes of many plant species, and has been used to transfer low erucic acid and low glucosinolate content into lines and breeding populations of Brassica. 
Pedigree breeding and recurrent selection breeding methods are used to develop lines from breeding populations. Pedigree breeding starts with the crossing of two genotypes, each of which may have one or more desirable characteristics that is lacking in the other or which complements the other. If the two original parents do not provide all of the desired characteristics, other sources can be included in the breeding population. In the pedigree method, superior plants are selfed and selected in successive generations. In the succeeding generations the heterozygous condition gives way to homogeneous lines as a result of self-pollination and selection. Typically in the pedigree method of breeding five or more generations of selfing and selection is practiced: F1 to F2; F2 to F3; F3 to F4; F4 to F5, etc. For example, two parents that are believed to possess favorable complementary traits are crossed to produce an F1. An F2 population is produced by selfing one or several F1's or by intercrossing two F1's (i.e., sib mating). Selection of the best individuals may begin in the F2 population, and beginning in the F3 the best individuals in the best families are selected. Replicated testing of families can begin in the F4 generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F6 and F7), the best lines or mixtures of phenotypically similar lines commonly are tested for potential release as new cultivars. Backcrossing may be used in conjunction with pedigree breeding; for example, a combination of backcrossing and pedigree breeding with recurrent selection has been used to incorporate blackleg resistance into certain cultivars of Brassica napus. 
Plants that have been self-pollinated and selected for type for many generations become homozygous at almost all gene loci and produce a uniform population of true breeding progeny. If desired, the haploidy method can also be used to extract homogeneous lines. A cross between two different homozygous lines produces a uniform population of hybrid plants that may be heterozygous for many gene loci. A cross of two plants each heterozygous at a number of gene loci will produce a population of hybrid plants that differ genetically and will not be uniform.
The choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F1 hybrid line, open pollinated variety, etc.) A true breeding homozygous line can also be used as a parental line (inbred line) in a commercial hybrid. If the line is being developed as an inbred for use in a hybrid, an appropriate pollination control system should be incorporated in the line. Suitability of an inbred line in a hybrid combination will depend upon the combining ability (general combining ability or specific combining ability) of the inbred.
Various breeding procedures are also utilized with these breeding and selection methods. The single-seed descent procedure in the strict sense refers to planting a segregating population, harvesting a sample of one seed per plant, and using the one-seed sample to plant the next generation. When the population has been advanced from the F2 to the desired level of inbreeding, the plants from which lines are derived will each trace to different F2 individuals. The number of plants in a population declines each generation due to failure of some seeds to germinate or some plants to produce at least one seed. As a result, not all of the F2 plants originally sampled in the population will be represented by a progeny when generation advance is completed.
In a multiple-seed procedure, canola breeders commonly harvest one or more pods from each plant in a population and thresh them together to form a bulk. Part of the bulk is used to plant the next generation and part is put in reserve. The procedure has been referred to as modified single-seed descent or the pod-bulk technique.
The multiple-seed procedure has been used to save labor at harvest. It is considerably faster to thresh pods with a machine than to remove one seed from each by hand for the single-seed procedure. The multiple-seed procedure also makes it possible to plant the same number of seeds of a population each generation of inbreeding. Enough seeds are harvested to make up for those plants that did not germinate or produce seed. If desired the haploidy method can be used to extract homogeneous lines.
Molecular markers including techniques such as Isozyme Eletrophoresis, Restriction Fragment Length Polymorphisms (RFLPs), Randomly Amplified Ploymorphic DNAs (RAPDs), Arbitrarily Primed Polymerase Chain Reaction (AP-PCR), DNA Amplification Fingerprinting (DAF), Sequence Characterized Amplified Regions (SCARs), Amplified Fragment Length Polymorphisms (AFLPs), Simple Sequence Repeats (SSRs) and Single Nucleotide Polymorphisms (SNPs) may be used in plant breeding methods. One use of molecular markers is Quantitative Trait Loci (QTL) mapping. QTL mapping is the use of markers, which are known to be closely linked to alleles that have measurable effects on a quantitative trait. Selection in the breeding process is based upon the accumulation of markers linked to the positive effecting alleles and/or the elimination of the markers linked to the negative effecting alleles from the plant's genome.
Molecular markers can also be used during the breeding process for the selection of qualitative traits. For example, markers closely linked to alleles or markers containing sequences within the actual alleles of interest can be used to select plants that contain the alleles of interest during a backcrossing breeding program. The markers can also be used to select for the genome of the recurrent parent and against the markers of the donor parent. Using this procedure can minimize the amount of genome from the donor parent that remains in the selected plants. It can also be used to reduce the number of crosses back to the recurrent parent needed in a backcrossing program. The use of molecular markers in the selection process is often called Genetic Marker Enhanced Selection or Marker Assisted Selection (MAS).
The production of double haploids can also be used for the development of inbreds in the breeding program. In Brassica napus, microspore culture technique is used in producing haploid embryos. The haploid embryos are then regenerated on appropriate media as haploid plantlets, doubling chromosomes of which results in doubled haploid plants. This can be advantageous because the process omits the generations of selfing needed to obtain a homogygous plant from a heterozygous source.
A pollination control system and effective transfer of pollen from one parent to the other offers improved plant breeding and an effective method for producing hybrid canola seed and plants. For example, the ogura cytoplasmic male sterility (cms) system, developed via protoplast fusion between radish (Raphanus sativus) and rapeseed (Brassica napus) is one of the most frequently used methods of hybrid production. It provides stable expression of the male sterility trait (Ogura 1968), Pelletier et al. (1983) and an effective nuclear restorer gene (Heyn 1976).
In developing improved new Brassica hybrid varieties, breeders use self-incompatible (SI), cytoplasmic male sterile (CMS) and nuclear male sterile (NMS) Brassica plants as the female parent. In using these plants, breeders are attempting to improve the efficiency of seed production and the quality of the F1 hybrids and to reduce the breeding costs. When hybridization is conducted without using SI, CMS or NMS plants, it is more difficult to obtain and isolate the desired traits in the progeny (F1 generation) because the parents are capable of undergoing both cross-pollination and self-pollination. If one of the parents is a SI, CMS or NMS plant that is incapable of producing pollen, only cross pollination will occur. By eliminating the pollen of one parental variety in a cross, a plant breeder is assured of obtaining hybrid seed of uniform quality, provided that the parents are of uniform quality and the breeder conducts a single cross.
In one instance, production of F1 hybrids includes crossing a CMS Brassica female parent, with a pollen producing male Brassica parent. To reproduce effectively, however, the male parent of the F1 hybrid must have a fertility restorer gene (Rf gene). The presence of a Rf gene means that the F1 generation will not be completely or partially sterile, so that either self-pollination or cross pollination may occur. Self pollination of the F1 generation to produce several subsequent generations is important to ensure that a desired trait is heritable and stable and that a new variety has been isolated.
An example of a Brassica plant which is cytoplasmic male sterile and used for breeding is ogura (OGU) cytoplasmic male sterile (R. Pellan-Delourme et al., 1987). A fertility restorer for ogura cytoplasmic male sterile plants has been transferred from Raphanus sativus (radish) to Brassica by Instit. National de Recherche Agricole (INRA) in Rennes, France (Pelletier et al., 1987). The restorer gene, Rf1 originating from radish, is described in WO 92/05251 and in Delourme et al., (1991). Improved versions of this restorer have been developed. For example, see WO98/27806 Oilseed brassica containing an improved fertility restorer gene for ogura cytoplasmic male sterility which is hereby incorporated by reference.
Other sources and refinements of CMS sterility in canola include the Polima cytoplasmic male sterile plant, as well as those of U.S. Pat. No. 5,789,566, DNA sequence imparting cytoplasmic male sterility, mitochondrial genome, nuclear genome, mitochondria and plant containing said sequence and process for the preparation of hybrids; U.S. Pat. No. 5,973,233 Cytoplasmic male sterility system production canola hybrids; and WO97/02737 Cytoplasmic male sterility system producing canola hybrids; EP patent application 0 599042A Methods for introducing a fertility restorer gene and for producing F1 hybrids of Brassica plants thereby; U.S. Pat. No. 6,229,072 Cytoplasmic male sterility system production canola hybrids; U.S. Pat. No. 4,658,085 Hybridization using cytoplasmic male sterility, cytoplasmic herbicide tolerance, and herbicide tolerance from nuclear genes; all of which are incorporated herein.
Promising advanced breeding lines commonly are tested and compared to appropriate standards in environments representative of the commercial target area(s). The best lines are candidates for new commercial lines; and those still deficient in a few traits may be used as parents to produce new populations for further selection.
For most traits the true genotypic value may be masked by other confounding plant traits or environmental factors. One method for identifying a superior plant is to observe its performance relative to other experimental plants and to one or more widely grown standard lines. If a single observation is inconclusive, replicated observations provide a better estimate of the genetic worth.
Proper testing should detect any major faults and establish the level of superiority or improvement over current lines. In addition to showing superior performance, there must be a demand for a new line that is compatible with industry standards or which creates a new market. The introduction of a new line commonly will incur additional costs to the seed producer, the grower, the processor and the consumer, for special advertising and marketing, altered seed and commercial production practices, and new product utilization. The testing preceding release of a new line should take into consideration research and development costs as well as technical superiority of the final line. For seed-propagated lines, it must be feasible to produce seed easily and economically.
These processes, which lead to the final step of marketing and distribution, usually take from approximately six to twelve years from the time the first cross is made. Therefore, the development of new lines such as that of the present invention is a time-consuming process that requires precise forward planning, efficient use of resources, and a minimum of changes in direction.
Further, as a result of the advances in sterility systems, lines are developed that can be used as an open pollinated variety (ie. a pureline cultivar sold to the grower for planting) and/or as a sterile inbred (female) used in the production of F1 hybrid seed. In the latter case, favorable combining ability with a restorer (male) would be desirable. The resulting hybrid seed would then be sold to the grower for planting.
The development of a canola hybrid in a canola plant breeding program involves three steps: (1) the selection of plants from various germplasm pools for initial breeding crosses; (2) the selfing of the selected plants from the breeding crosses for several generations to produce a series of inbred lines, which, although different from each other, breed true and are highly uniform; and (3) crossing the selected inbred lines with different inbred lines to produce the hybrids. During the inbreeding process in canola, the vigor of the lines decreases. Vigor is restored when two different inbred lines are crossed to produce the hybrid. An important consequence of the homozygosity and homogeneity of the inbred lines is that the hybrid between a defined pair of inbreds will always be the same. Once the inbreds that give a superior hybrid have been identified, the hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred parents is maintained.
Combining ability of a line, as well as the performance of the line per se, is a factor in the selection of improved canola lines that may be used as inbreds. Combining ability refers to a line's contribution as a parent when crossed with other lines to form hybrids. The hybrids formed for the purpose of selecting superior lines are designated test crosses. One way of measuring combining ability is by using breeding values. Breeding values are based on the overall mean of a number of test crosses. This mean is then adjusted to remove environmental effects and it is adjusted for known genetic relationships among the lines.
Hybrid seed production requires inactivation of pollen produced by the female parent. Incomplete inactivation of the pollen provides the potential for self-pollination. This inadvertently self-pollinated seed may be unintentionally harvested and packaged with hybrid seed. Similarly, because the male parent is grown next to the female parent in the field there is also the potential that the male selfed seed could be unintentionally harvested and packaged with the hybrid seed. Once the seed from the hybrid bag is planted, it is possible to identify and select these self-pollinated plants. These self-pollinated plants will be genetically equivalent to one of the inbred lines used to produce the hybrid. Though the possibility of inbreds being included in hybrid seed bags exists, the occurrence is rare because much care is taken to avoid such inclusions. These self-pollinated plants can be identified and selected by one skilled in the art, either through visual or molecular methods.
Brassica napus canola plants, absent the use of sterility systems, are recognized to commonly be self-fertile with approximately 70 to 90 percent of the seed normally forming as the result of self-pollination. The percentage of cross pollination may be further enhanced when populations of recognized insect pollinators at a given growing site are greater. Thus open pollination is often used in commercial canola production.
Currently Brassica napus canola is being recognized as an increasingly important oilseed crop and a source of meal in many parts of the world. The oil as removed from the seeds commonly contains a lesser concentration of endogenously formed saturated fatty acids than other vegetable oils and is well suited for use in the production of salad oil or other food products or in cooking or frying applications. The oil also finds utility in industrial applications. Additionally, the meal component of the seeds can be used as a nutritious protein concentrate for livestock.
Canola oil has the lowest level of saturated fatty acids of all vegetable oils. “Canola” refers to rapeseed (Brassica) which as an erucic acid (C22:1) content of at most 2 percent by weight based on the total fatty acid content of a seed, preferably at most 0.5 percent by weight and most preferably essentially 0 percent by weight and which produces, after crushing, an air-dried meal containing less than 30 micromoles (μmol) per gram of defatted (oil-free) meal. These types of rapeseed are distinguished by their edibility in comparison to more traditional varieties of the species.